Optical semiconductor elements, such as light emitting diodes (LED), are used as indicators or light sources. Recently, their outputs have become higher and their wavelengths have been shorter, which causes a problem that resin materials present near the optical semiconductor elements are degraded due to light. Further, in a case where a material having a glass transition temperature which is above room temperature and below the reflow temperature is used as an underfill composition, such a problem occurs that a chip warpage occurs in a reflow process.
The following Patent Literatures 1 to 3 disclose, underfill resin compositions which are epoxy resin compositions comprising an epoxy resin, a curing agent, and a curing promoter, where a bisphenol A epoxy resin or bisphenol F epoxy resin is used as the epoxy resin. However, when the epoxy resin composition mainly comprising these epoxy resins is used as an underfill composition in an optical semiconductor device, such a problem occurs that an encapsulating resin is degraded to become yellow due to lighting of the optical semiconductor elements for a long time, which luminance significantly lowers.
Patent Literature 4 discloses a composition which comprises an epoxy resin derived from isocyanuric acid, as a heat-resistant and light-resistant epoxy resin composition for encapsulating light emitting elements. However, light resistance of the composition is insufficient, too.
Meanwhile, recently, sizes of molded package have become bigger, for instance, in Matrix Array Package (MAP) method and, therefore, warpage which takes place in curing of an encapsulating resin is a serious problem. Large warpage causes various problems in a package transfer step and a package cutting step. The afore-mentioned compositions are unsatisfactory also in this respect.    Patent Literature 1: Japanese Patent Application Laid-Open No. 2007-169445    Patent Literature 2: Japanese Patent Application Laid-Open No. 2009-155405    Patent Literature 3: Japanese Patent Application Laid-Open No. 2009-173744    Patent Literature 4: Japanese Patent Application Laid-Open No. 2005-306952